Medium voltage interrupting devices (circuit breakers, switches, fuses) and associated equipment (instrument transformers, bus bars, L.A., etc) are contained in switchgear housings which consist of a large steel box divided in separate compartments. Lockable arc-resistant doors are provided in front of the medium voltage compartments. The arc-resistant doors are designed and tested to provide the highest possible degree of protection to personnel standing in front of the doors against the effects of an short circuit arc occurring in atmospheric air within the medium voltage compartment.
The short circuit current can reach values of thousands of amperes and the can cause a powerful explosion which can blow of the doors, eject outside hot gases and particles that can injure or kill personnel close to the switchgear enclosure.
To prevent injuries the switchgear enclosures are made as arc-proof as possible. The door accessing the medium voltage compartment is the point of weakness. To overcome the possibility of short circuit by-products escaping through the door of the switchgear housing, the door is made of thick steel and usually bolted closed by a plurality of bolts along the periphery of the door. While this is effective in closing off the door and securing it from a high short circuit arc, it makes accessing the inside of the compartment very difficult since a great deal of time will be required to unbolt the door to open it.
Ordinary door locks as used on standard or high security doors are much more convenient to use. These doors' locking system generally comprise a handle portion which is coupled to one or more door latches which engage one or more corresponding keepers in the door frame. Turning or moving the door handle generally causes the latch, or latches, to disengage their respective keepers, unlocking the door and allowing the user to open the door. While this standard type of door lock is quit convenient to use, it is generally not suitable for use with medium voltage switchgear enclosures. Standard door locks of this type do not provide the security required by high current short circuits arcs up to 63 kA, and will generally result in the door being blown off the housing in the event of a high current arc. An improved door assembly but which is as secure and arc-proof as a bolted door is therefore required.